<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8" />
		<title></title>
		<style>
			body{
				margin: 10px auto;
				height: 400px;
				width: 400px;
				border: 1px red solid;
			}
			#box1{
			margin: 5px auto;
			height: 360px;
			width: 360px;
			background-color: aqua;
			border: 1px blue solid;
			}
			button{
				text-align: center;
				margin: 0 auto;
			}
			.sty{
				border-radius: 50%;
				background-color: aqua;
			}
		</style>
	</head>
	<body>
		
		<div id="box1"></div>
		<button>方形</button>
		<button>圆形</button>
		<script>
			let dv = document.getElementById('box1')
			let but = document.querySelectorAll("button")
			console.log(but)
		
			but[1].onclick =()=>{
				dv.style.borderRadius="50%"
			}
			but[0].onclick =()=>{
				dv.style.borderRadius=""
			}
		</script>
	</body>
</html>
